fix(cyclones): convert NHC movement speed from mph to knots

server/providers/cyclones.js

@@ -43,6 +43,11 @@ function number(value, min, max) {
   const n = Number(value);
   return Number.isFinite(n) && n >= min && n <= max ? n : null;
 }
+// CurrentStorms.json reports movementSpeed in miles per hour (intensity is in
+// knots); convert so `speedKt` means what it says.
+function knotsFromMph(mph) {
+  return mph === null ? null : Math.round(mph * 0.868976);
+}
 // NHC stamps an advisory with its nominal time (e.g. 03:00Z) and publishes it
 // up to about half an hour before; allow that, but not a clock far ahead.
 const EARLY_ADVISORY_MS = 90 * 60_000;
@@ -120,7 +125,7 @@ export function parseCycloneStatus(payload, now = Date.now()) {
       pressureHpa: number(raw.pressure, 800, 1100),
       movement: {
         directionDegrees: number(raw.movementDir, 0, 360),
-        speedKt: number(raw.movementSpeed, 0, 200),
+        speedKt: knotsFromMph(number(raw.movementSpeed, 0, 200)),
       },
       advisoryUrl: officialLink(forecast.url),
       outlookUrl: raw.id.startsWith('al')

src/data/cyclonesProxy.test.mjs

@@ -115,7 +115,8 @@ test('status retains official clocks, knots, source links and finite current pos
   assert.equal(storm.issuedAt, TIME);
   assert.equal(storm.positionAt, TIME);
   assert.deepEqual(storm.position, { longitude: -125.8, latitude: 15.5 });
-  assert.deepEqual(storm.movement, { directionDegrees: 255, speedKt: 12 });
+  // NHC publishes movementSpeed in mph: 12 mph is 10 kt.
+  assert.deepEqual(storm.movement, { directionDegrees: 255, speedKt: 10 });
   assert.equal(storm.windKt, 25);
   assert.equal(storm.pressureHpa, 1006);
   assert.match(storm.advisoryUrl, /^https:\/\/www\.nhc\.noaa\.gov\/text\//);